1. Field of the Invention
The present invention concerns flame-resistant polyolefinic fibres and films and the procedure for their preparation.
2. Discussion of the Background
Polyolefins are widely used in the production of manufactures such as films and fibres and the necessity for having flame-resistant polyolefinic products is strongly felt, particularly for safety reasons in the various fields where they are used, for example, in the textile industry.
Various flame-resistant additives have been proposed in the art to give polyolefins flame-resistant properties: these generally consist of organic compounds containing phosphorous or halogen or both or halogenated compounds combined with a metallic oxide, as described by J.W. Lyons, in "The Chemistry and Uses of Fire Retardants", Wiley Interscience 1970, pages 286-297.
The flame-resistant additives already known are not, however, entirely satisfactory, mainly because of their incompatibility with polyolefins and also the high amounts required to give the necessary flame-resistant characteristics.
Flame-resistant monomers such as phenyl hydroxymethylene phosphinic acid and its alkyl esters: ##STR1## (where R is hydrogen or a lower alkyl ), are described in U.S. Pat. No. 4,517,355 together with how they are used for making linear polyesters flame-resistant.
Oligomeric flame-resistant compounds having the formula: ##STR2## (where R has the above meaning and n has a value, or an average value which ranges from 2 to 50), are described in U.S. Pat. No. 4.812.502 together with how they are used for making linear polyesters flame-resistant.
In the European patent application no. 334.423 a linear copolyester is described, which is used as a flame-resistant agent and which contains in its macromolecule units deriving from: terephthalic acid; alkylenic glycol (C.sub.2 --C.sub.6); and phenyl hydroxymethylene phosphinic acid, in a ratio from 1:1:0.2 to 1:1:1, in which units (c) are distributed at random between units (a) and (b), obtained by the brief contact at melting conditions of a linear polyester derived from terephthalic acid and an alkylenic glycol (C.sub.2 --C.sub.6), with an oligomer (II).